Bedding and Cleavage, Oslo, Norway - Interpreted

The color differences in the strata here largely reflects layers of different composition, the bedding, with the lighter grey being composed of more pure limestone, and the darker grey of a calcite-clay mix (i.e. a marl). The cleavage traces here reflect a younger planar feature impressed on the rocks during tectonic deformation, and is likely a result of a microscopic alignment of new micas in the rock. This caused small bits to break away and solution to be enhanced along that alignment to produce the outcrop expression of the cleavage. It is evident mainly in the marls because they have the right composition to grow new micas during burial, whereas the more pure limestone does not. The angle between the cleavage plane and bedding says something about the intensity of deformation (more on this later in the course). This deformation was part of the Caledonian orogeny

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